There have been a variety of foams produced in the past. A first commonly produced foam is made from polystyrene and a second commonly produced foam is made from low density polyethylenes (LDPEs). The polystyrene foam is too brittle for some applications like protective packaging which require protection from multiple impacts. LDPE foams are generally considered to be resilient and non-brittle, which are desirable properties. It is desirable to improve the tear strength, tensile strength and overall toughness of the LDPE foams in certain applications including protective packaging of heavy, delicate, and valuable items, such as furniture.
LLDPE resins have desirable properties such as good tear strength, tensile strength and overall toughness. It is very difficult, however, to produce a LLDPE foam that is dimensionally stable. In fact, even a small amount of LLDPE added to, for example, a LDPE foam will produce a foam that is not dimensionally stable. Of course, it is very desirable to produce a foam that is dimensionally stable.
Film/foam laminates have been produced for many years. Film/foam laminates have comprised, for example, a polyethylenic film laminated to a low density polyethylenic (LDPE) foam. The film portion of the film/foam laminate has generally comprised a conventional Ziegler-Natta catalyzed LLDPE or a combination of the conventional Ziegler-Natta catalyzed LLDPE and a LDPE for applications such as protective packaging. These conventional LLDPEs are generally characterized by a polydispersity index, D=M.sub.w /M.sub.n, of from 4 to 8 and have a z-average molecular weight below about 600,000. The use of this conventional LLDPE in the film portion is desirable because it provides the film/foam laminate structure with tear strength, tensile strength and overall toughness that can not be attained by using LDPE alone. Additionally, LLDPEs are desirable because of their economical savings over LDPEs.
In contrast, the foam portion of the film/foam laminate has consisted essentially of LDPE. The foam portion has not included LLDPEs, other than in trace amounts, because of reasons such as the inability to produce a dimensionally stable foam.
Film/foam laminates that use a conventional LLDPE in the film portion have certain disadvantages. For example, the film/foam laminate that is not suitable for sale (i.e., scrap material) cannot effectively be re-used or recycled in economical quantities into either the film portion or the foam portion. This scrap material is not desired in the film portion because the scrap material contains a significant fraction of LDPE from the foam portion which significantly weakens the strength of the film/foam laminate. The scrap material cannot be incorporated into the foam portion because of the above-discussed problems associated with producing a dimensionally stable foam. If scrap material can be recovered, then this would significantly reduce or eliminate the costly disposal of the in-process scrap that is associated with the manufacture of film/foam laminates.